Receptor proteins are molecules inside a cell or on its surface on which ligands bind. A ligand is any substance (e.g. a hormone, drug, functional group) that binds specifically and reversibly to another chemical entity to form a large complex.
Receptor proteins found inside a cell are called internal receptors or intracellular receptors or cytoplasmic receptors.
They act as regulators of mRNA synthesis to mediate gene expression.
When a ligand binds to an internal receptor, the receptor changes in conformation and exposes on itself a site that can bind to DNA.
The receptor joined to the ligand moves into the nucleus where it binds to a specific site on the cell DNA. Once bound, it promotes the process of transcription where information is copied from DNA to mRNA
